Process for treating wet spun filaments with shrinking agents

ABSTRACT

A METHOD OF TREATING FILAMENTARY MATERIALS FORMED FROM DIFFICULTLY MELTABLE POLYMERS (AMIDE) AND PARTICULARLY TO THE STEP OF RELAXING THE SHAPED WET FORMED FILAMENT BY CONTACTING THE FILAMENT FOR A PERIOD OF TIME AND AT A TEMPERATURE SUFFICIENT TO IMPROVE THE DYE RECEPTIVITY OF THE FIBER WITH A STRONG INORGANIC ACID SHRINKING AGENT OF A SPECIFIED CONCENTRATION. MORE PARTICULARLY, AQUEOUS SOLUTIONS OF SULFURIC ACID, HYDROCHLORIC ACID AND PHOSPHORIC ACID ARE USED AS THE SHRINKING AGENT.

Jan. 26, 1971 R. G. QUYNN ETA]- PROCESS FOR TREATING WET SPUN FILAMENTS WITH SHRINKING AGENTS Filed June 16, 1965 RELAXATION ROLLS AQUEOUS SHRINK/N6 AGE/V 7' E. 6. AQUEOUS SUL FUR/C A CID OF A PARTICULAR CONCE/V TRA 7' ION PUMP 2 Sheets-Sheet 1 Jan. 26,1971

R. G. QUYNN ET AL PROCESS FOR TREATING WET SPUN FILAMENTS WITH SHRINKING AGENTS Filed June 16, 1965 2 Sheets-Sheet 2 ma wxfi 6E p A h uuw w u w uwmmmmswfi 1.lu.,lm.wmwnlmw 3 8m H 5,? [r1 q a L a ESQ H. v? X 36% E\ H amt 343% E63 b53839. mu wa h gssiw United States Patent 3,558,763 PROCES FOR TREATING WET SPUN FILAMENTS WITH SHRINKING AGENTS Richard G. Quynn and Saunders E. Jamison, Summit, and Simon E. sobering, West Orange, N.J., assignors to Celanese Corporation, a corporation of Delaware Filed June 16, 1965, Ser. No. 464,317 The portion of the term of the patent subsequent to Shine 18, 1985, has been disclaimed Int. Cl. B29c 25/00 US. Cl. 264210 4 Claims ABSTRACT OF THE DISCLOSURE A method of treating filamentary materials formed from difiicultly meltable polymers (amide) and particularly to the step of relaxing the shaped wet formed filament by contacting the filament for a period of time and at a temperature sufficient to improve the dye receptivity of the fiber with a strong inorganic acid shrinking agent of a specified concentration. More particularly, aqueous solutions of sulfuric acid, hydrochloric acid and phosphoric acid are used as the shrinking agent.

This invention relates broadly to the art of treating filamentary materials. More particularly it relates to the treatment of a particular class of filamentary materials in order to effect relaxation thereof and thereby alter their internal structure so as to improve their dye-receptivity and otherwise improve their useful properties. The invention is especially concerned with a chemical relaxation treatment of shaped, wet-formed, diflicultly-meltable polymers, especially fiber-forming (fiber-formable) condensation polymers having nitrogen and/ or oxygen atoms, and preferably both nitrogen and oxygen atoms, as a part of the polymer chain, e.g., high-melting polycarbonamides, particularly those melting above 275 C. such as polyhexamethylene terephthalamide. The scope of the invention also includes methods, more particularly continuous methods, wherein the aforementioned treatment is a part of the process of making the filamentary material.

By difficultly-meltable polymers as used herein are meant polymers that cannot be shaped easily using meltextrusion techniques because they tend to degrade materially and/or to polymerize further to a useless, in fusible mass when heated sufficiently to melt them.

It was known prior to the present invention that polymers to which this invention is applicable could be formed into shaped articles, specifically filaments or fibers. See, for example, US. Pats. 3,154,512 and -612 of Parczewski; 3,154,609, Cipriani; 3,154,610, Denyes; and 3,154,- 614, Epstein et al., each dated Oct. 27, 1964; and 3,179,- 618, Roberts, dated Apr. 20, 1965. However, none of these patents teaches or suggests the chemical-relaxation treatment with which this invention is concerned.

In producing synthetic filamentary materials by either the wet or dry process, it is common practice to improve the physical properties of the freshly formed filaments, e.g., in the form of a bundle or tow, by a series of processing steps which include washing to remove the solvent, stretching to orient the molecules along the fiber axis, drying (if the filaments have not previously been dried), and finally subjecting the filamentary material to relaxation, which is manifested by an actual shrinkage of the fiber. In general, these steps are required in order to obtain filaments having the desired physical characterice istics that are generally considered necessary for textile and other applications of the filamentary material. The relaxation or shrinkage step is usually a very critical step in the process because it is the step in which the desired denier is obtained; and, also, this step aids in controlling (or in some cases may substantially completely control) useful properties of the fiber such as dye-receptivity, strength characteristics, luster, and other properties.

Prior methods used or suggested for use in effecting relaxation of synthetic filamentary materials have included boiling in water, treating with steam under controlled conditions, and treating with various chemical agents. Some of these chemical agents, in the concentrations employed, have been swelling agents for the filamentary material while others have had no swelling effect upon the filaments.

The present invention is concerned with a particular chemical-relaxation treatment that we have found to be surprisingly and unobviously effective when applied to shaped, wet-formed, difiicultly-meltable polymers of the kind described in the first two paragraphs of this specification, and more fully later herein. The chemical treatment of this invention involves the use of aqueous solutions of strong mineral acids, such as hydrochloric, sulfuric and phosphoric acids under particular conditions, especially concentration of such an acid in a solvent medium, e.g., water. The time and temperature conditions of treatment are also important. Such a treatment, to the best of the applicants knowledge and belief, has nowhere been taught or suggested in the prior art.

Thus, US. Pat. No. 3,060,550 dated Oct. 30, 1962, merely discloses that the snag resistance and reduced luster (presumably an increase in voids) of nylon hose, and increased dye afimity and reduced seam slippage of nylon fabrics can be obtained, by treating such shaped polyamide articles with an aqueous solution containing HCl and one or both ZnCl and certain monohydric or polyhydric alcohols and/or certain organic acids. US. Pat. No. 2,876,524 dated Mar. 10, 1959, discloses a method of altering the physical characteristics of linear polyamide condensation polymers which comprises exposing such polymers to an atmosphere of substantially anhydrous hydrogen halide gas, specfically I-ICl gas, and then desorbing said gas from the polymer. US. Pat. No. 2,743,231 dated Apr. 24, 1956, discloses that the pretreatment of nylon fabrics in relaxed state at the boil in baths containing from 0.5 to 3% by weight of 5-chlorosalicyclic acid or hydroxytoluic acid improves the dyereceptivity of the nylon article for acid, direct and acetate dyes.

The novel features of the invention are set forth in the appended claims. The invention itself, however, will be more readily understood from the following more detailed description taken in connection with the accompanying drawing, which is illustrative of the invention, and wherein FIG. 1 illustrates schematically apparatus and process steps whereby the invention can be carried out continuously in a process which includes the formation of filamentary material; and

FIG. 2 is similar to FIG. 1, but differs therefrom by showing snubbing pins inside the spin bath instead of stretch rolls outside the bath for molecularly orienting the filamentary material along the fiber axis.

Broadly described, the instant invention provides a method which includes the step of relaxing a shaped, wetformed, diflicultly-meltable polymer which consists in contacting the said shaped polymer with an inorganic acid shrinking agent. This shrinking agent is selected from 3 the group consisting of aqeuous solutions of sulfuric acid, hydrochloric acid, and phosphoric acid in the following ranges of concentrations by weight:

(a) 51 to 58% H 80 preferably 54 to 57% H 80 (b) to 34% HCl, preferably to 34% HCl, and (c) 79 to 84% H PO preferably 82 to 84%, H PO The shaped, wet-formed, difficultly-meltable polymer, more particularly a wet-spun, filamentary, difficultly-meltable condensation polymer having repeating amide units as an integral part of the polymer chain, is contacted with the aforementioned shrinking agent for a period of time and at a temperature sufficient to alter the internal structure of the fiber as evidenced by a change in its properties, e.g., an improvement in dye-receptivity. Although this contact period sometimes may be less than A second, ordinarily it is at least about A second, more particularly at least about /2 second. The temperature of the shrinking agent during the treating period is within the range of from ambient temperature (2030 C.), preferably in certain cases a minimum of about C., up to about or C. The contact period, the temperature of the shrinking agent and the chosen concentration of acid in the aqueous solution thereof are sufiicient to at least partly clear (i.e., free), and preferably substantially completely clear or free, the shaped article of voids, i.e., to produce a void-free structure. Stated otherwise, the contact period, the temperature of the shrinking agent and the chosen concentration of acid in the aqueous solution thereof are sufficient to alter the internal structure of the filamentary material whereby the properties are altered. Specifically there is obtained an improvement in dyeability (dye-receptivity), especially toward acid and disperse dyes.

The treatement with the shrinking agent may be applied to the filamentary material while it is in a loose or freeto-shrink (i.e., lengthwise) state; or while it is being maintained at a constant length (i.e., while it is held taut so that an actual shrinkage in length is prevented); or while it is under appreciable tension, e.g., while being stretched between draw rolls.

The presence of microscopic and submicroscopic voids, to a greater or lesser degree, in shaped wet-formed difficultly-meltable polymers of the kind broadly described hereinbefore and more specifically hereafter is almost always a characteristic of the washed and dried, wetformed polymers in untreated state, that is, in the absence of a suitable relaxation treatment that effects an actual shrinkage (at least in diameter) of the polymer in filamentary or other shaped form. The shrinkage may also occur lengthwise when the treatment is applied to the filamentary material while it is in a loose form or is in other state such that it is free to shrink lengthwise.

The presence of the aforementioned voids is particularly apt to occur when the extrudable composition is a solution of the polymer dissolved in concentrated sulfuric acid (e.g., 75 to preferably 95 to 100%, by weight H 80 concentration), and the liquid coagulant or spin bath into which the aforesaid composition is extruded is aqueous sulfuric acid having an acid concentration lower than that in which the polymer is dissolved and such that the solution of the polymer is coagulated into a shaped article, such as gelled filamentary material. For example, the concentration of the H 80 in the liquid coagulating bath may be below 65%, more particularly below 60%, e.g., from 0l0% to 55-59%, but preferably within the range of from about 40% to 52 or 53% H 80 The presence of the aforementioned voids in the washed and dried shaped polymer is undesirable for several reasons. For example, such voids result or tend to result in a shaped article such as a spun filament or fiber that is either semi-dull or has an uncontrolled level of dullness. These characteristics are undesirable and restrict the marketability of the filamentary material and fabrics made therefrom.

The void structure also affects the dyeability or dyereceptivity of the shaped structure in some manner that is not clearly understood. It has interfered with efforts to determine substantivity, rates of dyeing and shade levels.

There is also some indication that the presence of voids lowers or tends to lower the tensile properties of the polymer in filamentary form. For example, it has been noted that an increasing level of void formation in filaments produced in the same spin bath (i.e., using various combinations of bath temperature and acid concentration in the aqueous H SO coagulating bath) coincides with decreasing tensile properties. It is also possible that the presence of voids has been responsible for often attaining only mediocre tensile-property improvement upon hot drawing filaments of the polymer.

THE SHAPED POLYMER The polymers that are wet-formed into filamentary or other shaped structures or bodies and then treated in accordance with this invention are difiicultly-meltable, fiberforming polymers. Preferably the treatment is applied to those polymers having repeating =NCO groups, more particularly NRCO groups where R represents hydrogen or a monovalent organic radical, e.g., a hydrocarbon radical such as a lower-alkyl radical. Such polymers include the difficultly-meltable polyamides such as those wherein the NRCO groups are attached to carbon atoms on each side; the polyurethanes which contain repeating =NCOO groups, more particularly groups; the polyureas which contain repeating NCON: groups, more particularly RNCONR groups; and similar condensation polymers.

There is no particular advantage in wet-forming, e.g., wet-spinning, many of the polymers of the classes broadly described in the preceding paragraph, more particularly those which are adapted to be melt-extruded through orifices, slots, or other shaped openings to form the shaped body. However, in the case of the high-melting or diflicultly-meltable polymers, such polymers must be wet-spun rather than melt-spun. Wet-spinning often leads to voids that adversely affect certain properties, e.g., dyeability, of the spun filaments or yarn. The present invention is a solution to this problem. It provides practical means for altering the internal structure of the polymer so as to remove such voids thereby to improve the dyeability, luster and other useful and desirable properties of the article; and, especially, to effect this result (that is, to provide a relaxation treatment in which the structure of the shaped article such as a fiber or filament is altered) as a step in a continuous process.

Thus, the treatment of the instant invention is most useful when applied to shaped articles formed of high-melting polymers, more particularly those melting above 210 C. and especially above 275 C.; polyurethanes and polyureas melting above 179 C., especially above 210 C.; and, in general, polymers having cyclic groups such as 1,4-cyclohexylene and/or heterocyclic groups such as piperazylene or an alkyl-substituted piperazylene group, e.g., 2-(lower-alkyl)piperazylene such as 2,5-dimethylpiperazylene, as an integral part of the polymer molecule.

Some contemplated polyamides are, for example, those having repeating structural units of the formula that result from the condensation of a dicarboxylic acid or a derivative thereof, e.g., a salt, acyl halide, or ester of such an acid, with a diamine, wherein the Rs, which may be the same or different, are hydrogen, or monovalent organic radicals, e.g., lower alkyl such as methyl or ethyl, and the Ys, which also may be the same or different, are divalent organic radicals such as alkylene, e.g., ethylene, tetramethylene or hexamethylene, arylene such as paraand meta-phenylene, paraand meta-xylylene, and

paraand meta diethylenebenzene, cycloalkylene such as 1,4-cyclohexylene and divalent heterocyclic radicals such as those derived from piperazine, and monoalkyland dialkylpiperazines, e.g., 2-methyland 2,5-dimethylpiperazines, and 2-ethyland 2,5-diethylpiperazines, wherein the open bonds are attached to the nitrogen atoms, and wherein the chemical structure of the polymer and/or the polymerization technique used is such that a relatively high-melting polymer is obtained.

An important group of polyamides within the above group, and to which the present invention is especially applicable in treating shaped articles wet-formed therefrom, includes those in which Y and/or Y is or contains a paraor meta-phenylene radical or a 1,4-cyclohexylene radical. Particularly important are condensation products of a diamine and terephthalic acid or a derivative of terephthalic acid, e.g., terephthalyl chloride or a dialkyl terephthalate. Some specific polymers within this latter group are poly (polymethylene) terephthalamides wherein the polymethylene groups contain from 2 to carbon atoms, inclusive, e.g., polyhexamethylene terephthalamide, polyoctamethylene terephthalamide, polytetramethylene terephthalamide, and polypiperazylene terephthalamide. Other polyterephthalamides are poly(o-, m-, and p-phenylene) terephthalamides, poly(o-, m-, and p-xylylene) terephthalamides and poly(o-, m-, and p-diethylene-phenylene) terephthalamides, the latter produced, for example, by condensing an esterforming derivative of terephthalic acid with para-bis(betaarninoethyl)benzene.

The relaxation treatment of this invention is applicable to the production of filaments and other shaped articles of high-melting polyamides of aromatic acids other than terephthalic acid, e.g., of isophthalic acid, 2,6-naphthalenedicarboxylic acid, p,p'-dicarboxydiphenyl, (p,p'-dicarboxydiphenyhmethane, phenylenediacetic acid, phenylenedipropionic acid, and phenylenedibutyric acid. The diamine moieties of these other aromatic carboxylic acids may be the same as in the aforementioned polyterephthalamides. Illustrative, then, of polyamides other than the polyterephthalamides are the polyisophthalamides, specifically polyethylene isophthalamide. The relaxation treatment of the present invention also may be employed in making shaped bodies from high-melting polyamides resulting from a condensation reaction between (a) alkylene dicarboxylic acids such as adipic acid and (b) cyclic diamines such as p-Xylene diamine and p-bis(aminoethylbenzene).

Also contemplated is the relaxation treatment of shaped, hi gh-melting, autocondensation polymers (e.g., those melting above 275 C.) of an aminocarboxylic acid or a lactam or other derivative of such an acid, which polymers have repeating structural units of the formula wherein R and Y are as defined above. Some specific polyamides melting above 275 C. within this group are polymers of the following: l-carboxymethyl-4-aminocyclohexane or its lactam, 1-carboxy-4-aminocyclohexane or its lactam and 1-carboxymethyl-3-aminocyclopentane or its lactam.

Polyurethanes that may be wet-formed and treated in accordance with this invention are polymers having repeating structural units of the formula and resulting, for example, from the condensation of a diisocyanate with a dihydric alcohol or phenol or the condensation of a diamine with a bis(chloroformate) of a dihydric alcohol or phenol, where the Rs and Ys are as described above in connection with the polyamides, and the chemical structure of the polymer and/or the polymerization techniques used are such that a polymer melting above 179 C., preferably above 210 C., is obtained. Particularly useful, and shaped articles of which may be relaxation-treated in accordance with this invention, are polyurethanes prepared from dihydric alcohols or phenols containing a metaor para-phenylene or a 1,4- cyclohexylene radical. Some specific, shaped polyurethanes which may thus be treated are the condensation product of piperazine with the bis(chloroformate) of bis(p-hydroxyphenyl)propane-2,2, the condensation product of piperazine with the bis(chloroformate) of hydroquinone and the condensation product of tetramethylene diamine with the bis(chloroformate) of butanediol-l,4, each of which has a melting point above 210 C.

Polyureas that may be wet-formed and subjected to the relaxation treatment of this invention include those having repeating structural units of the formula wherein the Rs and Ys are as defined above. They may be synthesized, for example, by the addition of a diisocyanate to a diamine, the condensation of a diurethane with a diamine, the condensation of a carbon oxyhalide, such as phosgene with a diamine, or by heating an alpha, beta-diurea with a diamine, the chemical structure of the polymer and/ or the polymerization technique being such that a polymer melting above 179 0., preferably above 210 C., is obtained. Some specific polyureas that may be employed in practicing this invention are those obtained from the reaction of hexamethylene diisocyanate with hexamethylene diamine and from the reaction of m-phenylene diisocyanate with m-phenylene diamine, each of which polyurea melts above 210 C.

APPLICATION OF SHRINKING AGENT The aqueous inorganic acid treating of shrinking agents used in practicing this invention have been described hereinbefore. Any suitable means may be employed in contacting the shaped or fabricated polymer wit the shrinking agent. For example, the shrinking agent may be applied by immersing the shaped polymer in the aqueous solution of the inorganic acid constituting the treating agent; by spraying or dripping the shrinking agent upon the shaped structure, e.g., continuously moving filaments, especially when they are continuously advancing in a helical path over skewed rolls; or by brushing, padding or other conventional techniques for applying liquids to solid structures or substrates.

The shaped polymer in filamentary, film, fabric or other form may be treated batchwise or in semi-contlnuous or continuous operations. A continuous method of treatment is preferred, especially when the shaped polymer is of continuous (i.e., indefinite) length as in, for example, continuous filamentary materials such as threads, tows, films and fabrics of continuous length, and others.

In general, the application temperatures (i.e., the temperature at which the shrinking agent is applied) are Within the range of from ambient temperature (usually 20-30 C.) up to the boiling point of the shrinking agent at atmospheric pressure. Thus the upper limit may be about 100 C., but usually is not higher than about or C. The time of the treatment was briefly discussed hereinbefore with particular reference to the broad results sought to be achieved, that is, to alter or change the lnternal structure of the polymer so that at least certain properties of the shaped article are changed (e.g., an improvement in dye-receptivity) and the article is rendered clear or almost entirely clear of voids. The following additional discussion on this and related operating parameters may be helpful in better understanding the invention.

The period of time that the shrinking agent remains in contact with the shaped polymer, under particular conditions of temperature and concentration of the inorganic acid in an aqueous solution thereof, is in all cases sufiicient to improve the useful and desirable properties, especially dye-receptivity, of the treated polymer. It is difficult to state this time period with exact precision since there are so many different variables that may infiuence it. These include the constitution of the polymer being treated, its denier if in filamentary form or its thickness if in film, sheet or other form, the particular wet-forming technique employed, the temperature at which the shrinking agent is applied, the particular acid concentration of the shrinking agent, whether the polymer is in gelled or dried state, washed or unwashed, and other influencing factors.

For obvious reasons, it is desirable that the time and temperature employed in applying the aqueous shrinking agent, and the concentration of acid in said shrinking agent, are not such as will result in excessive softening of the shaped polymer, and especially when the latter is in the form of multifilamentary material. Such excessive softening can lead to coalescence (i.e., sticking or fusing together) of the individual filaments, which is undesirable.

The available evidence indicates that the contact time at the application temperature and concentration of acid in the shrinking agent should, for optimum results, be sufficient to result in complete or almost complete penetration of the shaped polymer by the treating agent. At ambient temperature treatments this time is usually less than 3 minutes and may be above A second or lower (that is, almost instantaneously) with certain shrinking agents, e.g., aqueous 57.5%, by weight, H 80 in order to avoid or minimize fiber coalescence. Microscopic observations show that progressive clearing of the microscopically visible voids coincides with penetration of the shrinking agent.

The upper time limit at the application temperature is critical only to the extent that it should not be so long as to cause excessive dissolution of the shaped polymeric article or otherwise adversely affect its useful properties. For example, the time should not be so long as to result in excessive (if any) coalescence of individual filaments of a multifilamentary material. In this connection it may be mentioned that a prelude to dissolution is sometimes evidenced by surface cracking or incipient fibrillation of treated filamentary material. In the case of those shrinking agents used in practicing this invention that have little or no solvation effect upon the polymer at the concentrations used, and depending also upon other influencing variables such as those mentioned hereinbefore, the maximum treating time in some cases may be as long as 12 to 24 hours, or even 2 or 3 days or more, provided that there are no adverse effects such as those pointed out hereinbefore.

The relaxation treatment of this inventory may be applied to the washed and dried filamentary material; or to the washed but undried, i.e., never dried prior to the relaxation treatment) filamentary material; or to the freshly spun, unwashed, gelled filamentary material containing solvent from the spinning dope and/or liquid coagulant from the spin bath, e.g., aqueous sulfuric acid. The treatment is especially adapted for use in a continuous method of producing relaxed filamentary material, e.g., as illustrated in FIGS. 1 and 2 of the drawing, and which includes the steps of wet-forming, more particularly wet-spinning, a solvent solution of a difiicultly-meltable polymer of the kind with which this invention is concerned thereby to obtain a shaped article; and contacting the shaped polymer or article with an inorganic acid shrinking agent of the kind used in practicing the present invention, and in the manner hereinbefore described in order to alter its structure and thereby improve its properties, especially dyeability. The effect of the treatment is, in general, an improvement in the luster and appearance of the fiber (especially when the shaped article has a high content of voids), and a dyeability (dye-receptivity) improvement as exemplified by an increased take-up of dyestuffs such as acid and disperse dyestuffs.

Illustrative of the results obtained by using the relaxation step of the invention in a continuous process is the following: A two-pound lot of 40-filan1cnt dycable relaxed polyhexamethylene terephthalamide (6-T) yarn was produced by continuously extruding a sulfuric acid solution of the polymer into an aqueous coagulating bath of sulfuric acid having a concentration of H 50, less than that used in dissolving the polymer. The resulting gelled filamentary material was continuously oriented by snubbing about 40-80, more particularly about 70, in the coagulating bath, and further continuously processed (treated with sulfuric acid shrinking agent of the concentration employed in this invention, water-washed and taken up) as illustrated in FIG. 2. When dyed in an infinite dye bath of the acid dye Alizarin Sky Blue BS-CF (C.I. No.: Acid Blue 78) a sample of control yarn, which had been processed in substantially the same way as above set forth except that it had not been subjected to treatment with the sulfuric acid shrinking agent, showed a dye uptake of only 1.0%. In marked contrast the above-described relaxed yarn resulting from treatment with the sulfuric acid shrinking agent showed a dye uptake of 2.3% when subjected to the same dye test.

With further reference to the use of the applicants relaxation step in a continuous process, the following additional observations are presented.

It is desirable to use as the acid shrinking agent one that has the same chemical constitution as that of the chemical agent(s) already in the process, thereby minimizing storage and recovery problems. For instance, when concentrated sulfuric acid is employed as a solvent for the polymer, and less concentrated aqueous sulfuric acid is used as the coagulating bath, then it is advantageous both economically and process-wise to use a sulfuric acid shrinking agent. The same remarks apply to the other inorganic acid shrinking agents employed in practicing this invention, especially phosphoric acid.

A requirement for a successful continuous process that includes a continuous relaxation step is a rate of action of the shrinking agent rapid enough for practical coordination with the desired throughput rates of the spinning operation and to effect this result without excessive or severe fiber damage.

In order that those skilled in the art may better understand how the present invention can be carried into effect, the following examples are given by way of illustration and not by way of limitation. All parts and percentages are by weight unless otherwise stated.

Example 1 The polymer employed in this example was a poly- (polymethylene) terephthalamide, specifically polyhexamethylene terephthalamide (6-T). The solvent for the polymer in making the spinning solution or dope was concentrated sulfuric acid in weight percentages (as 100% H 80 ranging from 81.8 to 86.0. The concentration of polymer in this solvent ranged from 10.0 to 12.1. The Brookfield viscosity at 25 C. (4 r.p.m.) ranged from 3100 poises to 5880 poises. Usually ammonium sulfate was added in an amount ranging from 4.4 to 5.4% (based on the weight of the solvent) in order to reduce the tendency of the filamentary material to rupture during coagulation. This additive is soluble in concentrated sulfuric acid and is exemplary of additives that are capable of yielding basic bodies in solution that have an affinity for protons equal to or greater than that of bisulfate ions. Other examples of such additives and the advantages of their use in spinning filaments from concentrated sulfuric acid solutions of a polymer of the kind employed in this invention are given in the aforementioned US. Pat. No. 3,154,613.

A typical method of making the dope is as follows:

The ammonium sulfate is added to the concentrated sulfuric acid at room temperature (2030 C.,), and the mixture is stirred at the same temperature until the ammonium sulfate goes intosolution. The polyhexamethylene terephthalamide in finely divided state is added to, and admixed with, the solution of ammonium sulfate in the sulfuric acid. Mixing is effected at about 40 -50 C., and is continued until the polymer has substantially completely dissolved, e.g., for about 2 hours. The inherent viscosity of the polymer component of the dope varies, for example, from 1.5 to 2.5, and is preferably within the range of from 1.8 to 2.5, measured as a solution of 0.4 gram of polymer per deciliter of concentrated sulfuric acid solvent at 25 C.

The dope compositions and viscosities are given in Table I.

agent, the treated yarn was washed by dripping hot water and by partial immersion in hot water, and was then taken up on perforated viscose bobbins under a hot water drip.

Tables II-A and II-B illustrate the results of continuous spinning and relaxation of IO-filament 6-T yarn, using snubbing pins or stretch rolls to effect orientation of the molecules along the fiber axis and aqueous sulfuric acid of the kind employed in this invention as the shrink- 10 ing agent. The spinning and relaxation conditions are TABLE I.DOPE COMPOSITIONS AND VISCOSITIES Dope Number .I-35 .I-37 .I-38 .I-39 .I-43 J44 .I-56 S-35 8-36 S-38A 8-41 8-43 Polymer concentrated, weight percent 10.0 11.0 10.0 11. 11.0 11.0 12.0 11.0 12. 1 11.2 10.6 10.6 Sulfuric acid, weight percent as 100% acid 83.5 82.6 83. 82.6 82.6 82. G 86.0 82.8 81. 8 82.6 82. 4 82. 4 Water, weight percent 2.0 1. 9 2.0 1. 9 1. 9 1. 9 2.0 1. 8 1. 7 1. 7 1. 6 1. 7 Brookfield viscosity at 25 C. (4

rpm.) poises 3, 100 5, 100 3, 300 6, 700 5, 880 5, 600 5, G00 3, 600 4, 250 3, 700 4, 100 5, 100 (NH4)2S04, weight percent on solvent 4. 5 4. 5 4. 5 4. 5 4. 5 4. 5 0 4. 4 4. 4 4. 5 5. 4 5. 4

A dope bomb under nitrogen pressure was used in feeding the dope to the spinnerette. An aqueous sulfuric given in Table 'IIA, and the physical characteristics and results of dye tests in Table II-B.

TABLE IIA.GONTINUOUS SPINNING AND RELAXATION OF IO-FILAMENT ti-T YARN Coagulation bath Treatment conditions Bath Concen- Snub- Concen- Spin trated Temperabing trations, Temperaspeed, H2804, ture, angle, Stretch HzSO4, ture, Time Run No. Dope m./min. percent C. ratio percent O. minutes acid coagulating bath circulated through a fectangll' TABLE II-B.PHYSICAL CHARACTERISTICS AND BE- lar trough formed of clear poly(methyl methacrylate) by an external Jabsco pump equipped with a by-pass. Constant temperature in the coagulating bath was maintained with a glass-enclosed electric heater and a glass-enclosed thermoregulator. When used for orientation of fibers, snubbing pins (see FIG. 2) were applied to the bath vertically from above. The pins comprised a pair of %ll'lCh Alsimag rods held %-inch between centers in a 2-hole rubber stopper which was fixed in a clamp above the bath. The stopper was rotated to provide the desired snubbing angle.

The yarn was advanced over skewed rolls, the speed of which was adjusted by means of Heller or Graham drive systems. The first pair of rolls after the coagulating bath were each 2 inches in diameter. These were followed, when used with stretching (see FIG. 1), by another pair of 2-inch rolls. The rolls preceding the acid-treatment rolls were run at the same speed as the latter. The rolls of the next pair were cylinders covered with Synthane laminate, which is an acid-resistant laminated material. Both rolls were 13 inches long, one roll being inches and the other 2 inches in diameter. The lower of the rolls was partially immersed in the trough of aqueous inorganic acid shrinking or treating acid. The smaller roll was immersed over a length of about 1 inch in test runs with 10-filament yarns, while the larger roll was immersed over a length of 8 inches in the test runs made with 40-fi1arnent yarns. The total length per wrap was inches and the total roll residence time was about seconds. The yarn was thus immersed at the indicated temperature for only either or M of the total roll residence, although it was wetted by entrainment of the acid-treating solution for the entire period.

In carrying out the runs with -filament yarn the bath of treating acid was circulated through an external reservoir by two adjustable-speed Jabsco pumps.

On a second pair of Synthane-covered rolls similar to those described above for applying the acid shrinking SULTS OF DYE TESTS ON THE 10-FILAMENT (i-T YARNS FROM THE RUNS DESCRIBED IN TABLE II-A Dye uptake* Ten- Elonga- Modu- Run acity, tion lus, Dis- No. Denier g./d. percent 'IE g./d. perse Acid *Measured as percent by weight of dry fiber. Disperse dyestutf is Alizarin Sky Blue BS-CF.

From the data presented in Tables II-A and II-B, it will be seen that the relaxation or clearing of voids that is obtained by the treatment with the sulfuric acid shrinking agent provides a marked improvement in the dyeability of the fibers as compared with the controls, that is, samples from similar runs wherein the filamentary material had not been relaxed. For example, the acid dye take-up of the yarn from Run 583 was 4.2% and from Run 71-5, 3.5% as compared with 1.5% and 0.6%, respectively, for the acid dye take-ups for the yarns from the corresponding controls. There was an increase in percent elongation and a moderate decrease in tenacity. The overall physical properties were good, and there was no evidence of any marked physical damage to the yarns as a result of the acid treatment.

The data in Table III show the progressive effect of increased concentration and/ or temperature of the sulfuric acid shrinking agent .in the relaxation treatment of 40-fil./1.5 d.p.f. 6-T filament yarn that was spun from Dope No. S-38A (see Table I). Whether snubbed or stretched, the continuous response to increase of temperature and concentration provides up to 3.6 or 3.7% uptake of the acid dye Alizariu Sky Blue BS-CF by filaments of about 3.7 g./d. tenacity, as compared with 0.9 and 1.0 acid dye uptake for the corresponding controls.

TABLE I1I.CONT1NUOUS SPINNING AND RELAXATION OF -FILAMENT 1.5DPF YARN AND PROPERTIES OF RELAXED YARN Coagulat- Treatment conditions Tensile properties mg bath Bath conccntra- Snubconcentration, in; on, Tempera- Elonga- Acid Spinning IIzSO4, Stretch angle, HzSOs, ture, Time, Tenacity, tion, dye sample No. percent ratio percent C. minutes Denier g./d. percent TE uptake 47.1 (4) 2 1.7 5.1 18.2 21.6 0.9 47.1 55. G 47 0.5 1.6 4.0 23.0 19. 3 2. 7 47. 1 55. S) 55 0. 4 1. 5 3. 7 25. 3 18. 4 3. 6 47.3 1.6 5.2 26.1 26.7 1.0 47. 3 5G. 2 0. 5 1. 5 4.1 25. 4 20.8 2. 9 47. 3 56. 1 0. 5 1. 6 3. 7 33. 4 21. 2 3. 7

In general, orientation of the filaments by snubbing gives better dye-receptivity when spinning 6-T polymer than when orientation is eifected by stretching, and avoids excessive stripping of the fibers on the stretch rolls at the draw ratios normally required for development of adequate tensile properties of the filaments. Draw ratios should preferably be below 3.25 (e.g., from 2.5 to 3.2) to assure effective shrinking action of the acid-treating agent on the filaments.

The dripping of hot rinse water on the stretch rolls preceding the acid-treatment rolls seems to have little influence, if any, on the physical properties of the yarn. An increase in the acid-treating temperature from 50 to 55 C. results in a substantial improvement in both acid-dye and disperse-dye uptake, especially the latter. In this connection see the data on Run Nos. 7712 and 77-13 in Tables IVA and IV-B, and compare each with the control (Run No. 77-1).

In the runs shown in Tables IV-A and IV-B, filtered dope 841 (see Table I) was spun at 50 m./ min. through a 40-hole jet, 1 inch in diameter, and having holes 0.15 mm. in diameter. The immersion time of the yarn in the aqueous sulfuric acid shrinking agent was 0.17 minute, and the traverse time was /2 minute.

1 l geasured as percent of weight of fiber o1 Alizarin Sky Blue BS-CF. 1 one.

TABLE IV-Br-PI'IYSICAL CHARACTERISTICS AND THE RESULTS OF DYE TESTS ON THE 40-FILAMEN'I (y-T YARNS FROM THE RUNS DESCRIBED IN TABLE IV-A Tensile properties *See footnote to Table II-B.

With snubbing at 70 stable spinning of 40-filament 6-T yarn was maintained at 65 packages, each collected over a period of 30 minutes of continuous spinning, snubbing and relaxation, were produced. The dope that was spun corersponded to that of Dope No. 8-41 (see Table I). The concentration of the aqueous sulfuric acid treating agent ranged between 55.5 and 56.1%, and the treating or application temperature was -80 C. The average and the extreme properties of the relaxed yarn and of the control (i.e., not treated with the aqueous sulfuric acid treating agent) are given in Table V.

TABLE V [Ranges of properties of 40-filament 6T relaxed and unrelaxed yarn collected during a 33%-liour run] Treatment conditions Uptake of Alizan'n Concentra- Sky Blue tion of Tenacity Elongation BS-CF, H2SO4, Tempera- Denier percent TEV percent; percent turc G.

Control:

Average 2. 8 4. 7 28 24. 9 1. Maximum- 3. 6 5. 4 35 28.0 1. Minimum 2. 2 4. 3 22 20. 3 0. Treated:

Average 2.8 3. 8 36 22. 2 2. 3 Maxinnnn. 3. 4 4. t) 49 2G. 7 3. 6 56.1 68 Minimum 2. 1 2. G 26 16. 2 1. 5 55. 5 (30 TABLE 1VA.-CONT1NU()US SPINNING, STRETCI'IING AND RELAXATION OF 40-FILAMENT 6-T YARNS When the acid-dye uptake is plotted against tenacity for the aforementioned packages of 40-filament 6-T yarn, a reasonably distinct negative correlation is observed despite the variability. The best fitting straight line on the basis of least squares computation has the equation:

where A represents the acid-dye uptake in weight percent and T represents tenacity in g./ d.

The results obtained by using higher temperatures and shorter contact times, c.g., from about M; to about V2 second) in treating 40-filament 6-T yarn with aqueous sulfuric acid in concentrations ranging between about 55.6 and 56.2% are given in Table VI. The spinning dope was spun at a speed of 30-50 m./min. through a 40-hole jet, 1 inch in diameter, and having holes 0.10 mm. in diameter. The extruded yarn was oriented by snubbing. Spinning at the aforementioned speed, the length of yarn immersed in the aqueous sulfuric acid was about 20-30 cm.

It will be noted form the data given in the table that the shorter contact time at higher temperaures results in less decrease in the tenacities and only moderately higher values for percent elongations on the treated yarns as compared with the control samples while providing a 3- to .5-fold increase in the percentage of acid-dye uptake.

TABLE VI The aqueous phosphoric acid and the aqueous sulfuric acid solutions employed in the above tests were at ambient temperature (about C.) during the period the loose 2.2-denier fiber was immersed therein.

The aqueous phosphoric acid solutions may be used in relaxing the various dried difficultly-meltable polymers Physical characteristics of -fiiament 6-T yarn produced continuously using higher temperatures and shorter contact times in applying aqueous sulfuric acid treating agent] Treatment bath Concen- Temperatration, Acid ture, percent Tenacity, Elongation, dye Run No H2804 Demer g./d. percent uptake 1 1 Weight percent on dry fiber of Alizarin sky blue BS-OF. 2 None.

Example 2 Repetition of the various runs of Example 1 using as the inorganic acid shrinking agent, an aqueous solution of phosphoric acid containing from 79 to 84%, more particularly from 80 to 84%, by weight of H PO' instead of an aqueous solution of sulfuric acid containing from 54 to 58% by weight of H SO similarly clears the filamentary yarn of voids and yields a relaxed yarn of improved dye-receptivity.

Microscopic observations of the action of various concentrations of phosphoric acid in clearing 2.2-denier 6-T fiber of voids are tabulated below:

Conc. H PO Time to clear (w./W.), percent in minutes 84.0 2

Visible damage to the fiber was noted after immersion in the 84% H PO for 6 minutes. When the loose fiber was immersed in the 83% H PO for 1 hour, there was no visible evidence of damage to the fiber.

The aqueous phosphoric acid solutions employed as a shrinking agent are less drastic in their action on the filamentary material that is treated in accordance with this invention than are the aqueous sulfuric acid solutions. This may be noted by comparing the time for clearing filaments of the 6-T yarn of voids using various concentrations of H PO with the clearing time tabulated below when employing aqueous solutions of H 50 in various concentrations on filaments of the same 6-T yarn.

in filamentary or other shaped form irrespective of the solvent or liquid coagulant employed in their preparation. However, if yarn relaxation is to be elfected by treatment with an aqueous phosphoric acid solution as a step in a continuous process, then it is preferred for economical and other reasons to use a solution containing more than e.g., from to by weight of H PO as a solvent for the polymer; and then extrude the resulting polymer solution or dope through a shaped opening into a liquid coagulant containing phosphoric acid in a lower concentration than that used in dissolving the polymer. This lower concentration is such that the dope, after passing through the shaped opening, is coagulated into a shaped article such as filamentary material.

Example 3 In the tests described under this example apparatus was set up for the continuous treatment of multifilament yarn with inorganic acid shrinking agent followed by a water-wash bath.

Yarn from a supply bobbin was passed through a tension gate and then over two pairs of skewed rolls, the first pair of which was immersed in the acid-treatment bath while the second pair was immersed in a water-wash bath. The wash rolls were operated at a speed just sufficiently greater than that of the treating rolls to draw the yarn through the system, so that no deliberate tensioning during treatment was employed. Takeup speeds varied from 3 to 8 m./min., and the residence time was altered by changing the number of wraps. Residence times were checked by timing the passage through the system of a knot tied to the incoming yarn. Washing in about 0.1 N aqueous sodium bicarbonate at the takeup bobbin was employed in certain instances indicated in the tables that follow. After takeup, bobbins were immersed in cold running water for several hours or overnight (about 16 hours).

In general the following three criteria, in addition to changes in dyeability, were used to establish that a significant degree of relaxation had been obtained by a given treatment:

(1) Removal of voids as judged by direct microscopic examination.

(2) Change of tensile properties in the direction of increasing elongation, and decreasing tenacity and modulus, together with a characteristic change of shape in the load-elongation curve.

(3) A characteristic change of certain features in the fiber X-ray pattern.

Criterion (1) cannot be used in checking freshly spun or gelled yarn, since the void structure is not detectable in such yarns.

The microdyeing technique (infinite dyebath) was used for obtaining dyeing data, except in one case where sutficient yarn was available for a finite (4%) dyeing. Instron data were collected at 3 /3 gauge length and min. chart speed, for better precision in the modulus measurement.

All acid treatments and washes were applied at ambient temperature (about C.).

Bobbins of initially dry 300/100 wet-spun 6T multifilament yarn were selected for the relaxation treatment of dry yarn. This yarn had an average tenacity of the order of 4.55 g./d. Although otherwise of fairly good quality, the filaments showed a characteristic, objectionable, skin/core void structure, and poor dyeability.

Preliminary estimates by microscopy of the times required for complete penetration of the 3d.p.f. fiber established an approximate concentration of reagent that would be required for effective void clearing in reasonable (e.g., less than 3 minutes) residence times. These observations were used as the basis for the series of continuous treatments, the results of which are given in Table VII. Aqueous hydrochloric acid containing 32% HCl was used in some runs, while 56%, 56.5% and 57.0% H SO were used in other runs. Runs were made both with and without a final aqueous sodium bicarbonate wash. No coalescence was noted with any of the systems shown in Table VII at the residence times specified. Eastone Red N-GLF and Interchemical (I/C) Blue B are disperse dyes while, as indicated hereinbefore, Alizarin Sky Blue BS-CF is an acid dye.

TABLE VII A series of three bobbins of initially dry multifilament 6T yarn was treated continuously in 55.7% H 30 (by analysis) at a residence time of 65 seconds to produce about 2100 meters of 300/100 yarn at a speed of 10 m./min. The takeup bobbin was being soaked in 0.1 N aqueous sodium carbonate as the yarn was collected, and the yarn was then washed separately in cold water on the bobbin for several hours. A small portion of the wet, collected yarn was allowed to dry at ambient (room) temperature, while another portion was oven-dried for 8 minutes at about 95 C. This test was conducted to ascertain whether or not the drying technique significantly affected the dyeability of the yarn. Hoselegs were knitted from the untreated yarn, and from treated yarn dried at room temperature. The dyeing results for yarn and hoseleg are given in Table VIII. It was noted that the hoseleg of treated yarn was distinctly more lustrous, and somewhat smoother to the touch, than the control hoseleg.

TABLE VIII [Dyeability of sulfuric acid-treated 6T multifilarnent as yarn and knitted hoseleg] Mierodyeing, 2 hrs. at 07 C. Percent dyestull, o.w.t.

Finite dyeing (4%), 2 hrs. at 07 0.; Percent dyestutl, o.w.f.

Eastone Alizarin Red Sky Blue Control liesclcg 0. 5 0. c

Treated hosclcg. 3. 5 2. 2

The relaxation treatment of this invention is also applicable for use in a semi-continuous process. For example, yarn can be wet-spun without including the relaxation treatment as a part of the process, and collected on bobbins after snubbing and/or stretching to orient the molecules along the fiber axis, the orientation step being preceded by or followed by washing (preferably the latter). The yarn is maintained in never-dried o1- gelled state, e.g., by keeping the bobbins immersed in water, until the relaxation treatment is applied.

The results of continuously treating such gelled yarns using the apparatus described earlier in this example are given in Table IX. The yarn employed was 40-filament 6T yarn spun from a sulfuric acid solution of 6T polymer by extrusion through a 40-hole jet into a hori- [Teusile and dyeing properties of relaxed dry 300/100 multifilament 6T yarn] Mierodyeing, 2 hrs. at 97 0. Percent dyestuti, o.w.f.

Eastone Alizarin Tenacity Elongation Modulus Red I/O Sky Blue Sample (g./d.) (percent) (g./d.) T13 NGLF Blue B B S-CF Control, 32% aqueous H01, 4. 6 12 80 15. 8 0.5 1. 1 0. 7

water washed:

17 second residence 3. 9 23 18. 6 6. 9 4. 9 2. 6 30 second resideuee 2. 7 30 60 15. 0 7. 4 5. 5 3. 2 1 minute residence 2. 3 30 51 12. 6 6. 5 4. 3 2.8 Control, 32% aqueous H01, 4. 7 21 90 21 2.8 0.8

aqueous sodium bicarbonate washed:

30 second residence 4. 1 23 84 20 8. 7 4. 3 Control, 56% aqueous H350 5. 1 16 20. 4 0.7 1.1 0.4

water washed:

30 second residence 3. 7 1t) 62 16.2 5. 3 3. 8 2. 3 1 minute residence 3. 6 23 60 17. 2 5. 3 4.0 2.0 2 minute residence 3. 7 25 59 18. 5 5. 6 4. 1 2. 3 Control, 56.5% aqueous H2504 4. 6 12 15. 8 0. 5 1. 1 0. 7

aqueous sodium bicarbonate washed:

30 second residence 3. 6 22 68 16. 5 5. 9 4. 6 2. 6 45 second residence" 3.0 23 64 14. 3 6.2 4. 8 3. 1 1 minute residence 3. 2 24 66 15. 7 6.6 4. 6 3.0 Control, 57.0% aqueous HzSO; 4. 0 14 84 19 1. 1 0. 0

aqueous sodium bicarbonate washed:

30 second residence zontal coagulating bath containing H 80 in a lower concentration than that used to dissolve the polymer but sufficient to coagulate the extruded dope. The extruded yarn was oriented by snubbing, washed, and taken up on bobbins that were kept in water.

No dyeings were made with Interchemical (I/C) Blue B since all previous work showed that the response of the fiber to this disperse dyestuff substantially paralleled that obtained with the disperse dye Eastone Red N-GLF. No coalescence of the fibers occurred under the conditions indicated in the table. The dyeability of the gelled filamentary material that was treated was greater than that of the dried 300/100 6-T yarn used in previous tests (see Table VII), but still commercially inadequate. Although the reason for this is unknown, it may be due to the fact that the spinning and drying conditions were different. The 40-filament gelled yarn was wet-spun into a horizontal trough; and, for the control fiber, dried at room temperature. On the other hand, the 300/100 filamentary yarn was downspun to obtain a gelled filamentary material which was hot dried. X-ray examinations showed the two types of control fibers to differ slightly in structure.

TABLE IX the fiber is brought close to the point of solution in the acid-treating agent. In general, it appears that the closer the fiber comes to dissolving, the more marked is the degree of relaxation and the greater is the dyeability improvement; additionally, the change in tensile properties is likewise more marked, so that in practice a compromise has to be made between tensile-property change and dyeability improvement.

When the acid-treating agent employed to effect relaxation is not used as a step in a continuous process that follows extrusion and coagulation with no intervening drying step, aqueous hydrochloric acid is superior to aqueous phosphoric and sulfuric acids, especially the latter, in such factors as, for example, luster, clarity, lack of cracking, effectiveness of short residence times and retention of tensile properties.

From the results of the tests in relaxing gelled filamentary materials, it will be noted that the presence of moisture in the filamentary material is no barrier to the effectiveness of the relaxation process. The only apparent effect of this moisture is its diluting action, so that somewhat higher concentrations of treating agent or longer [Tensile and dyeing properties of washed, gelled, relaxed -filament 6-1 yarn] Microdyeing, 2 hrs. at 97 0. percent dyestuff, o.w.f.

Eastone Alizarin Tenacity, Elongation, Modulus Red Sky Blue Sample (g./d.) (percent) (g./d.) TE N GLF BS-CF Control 3. 4 33 55 19. 3 2. 5 1. 8 57% H2504, Water and bicarbonate washed:

33 seconds residence 2. 5 31 59 13. 7 2. 7

seconds residence 2. 5 42 15. 9 e. 1 2. 9

1 minute residence 2. 4 37 56 14. 9 7. 3 3. 6

1.7 minutes residence 2. 6 35 63 15. 3 8. 5 3. 2 56.5% H2804, water and bicarbonate washed:

1 minute residence 3. 0 40 18. 7 6. 2 3. 7

2 minutes residence. 2. 6 33 57 14. 6 6. 2 3. 5

3.5 minutes residence 2. 3 48 50 16. 0 7. 2 3. 5

Microscopic observations were made on the void- 40 treatment times are usually necessary with gelled yarns clearing action at room temperature (about 25 C.) of 50/50 and 80/20 (v./v. in each case) of 37.2% HCl/H O on dried 300/ 100 multifilament 6-T yarn such as was used in previous tests. These volume ratios correspond, respectively, to weight ratios of about 20.3/ 79.7 and about 30.7/ 69.3 of 37.2% HCl/H O. Using the more dilute aqueous solution of HCl, there was no evidence of any void clearance after the filamentary material had been subjected to the action of the acid for 5 minutes. When the more concentrated solution of aqueous HCl was employed, the action of the acid in clearing the filamentary material of voids was complete in about 8 minutes.

The per cent dye uptake resulting from a given set of treatment conditions is approximately proportional to the volume fraction of the fiber penetrated and cleared of voids. The proportionality is more strictly adhered to when dyeing with disperse dyestuffs than with acid dyestuffs. The reason for this is not clearly understood but may be associated with either the constitution of the particular acid dyestuff employed or a difference in the mechanism between disperse and acid dyeing.

When practicing the present invention it can be shown by calculation that the volume fraction penetrated, AV/V, of a circular filament of the kind treated in accordance with the invention varies with the fractional radial penetration, p, according to the relationship This function can be plotted to illustrate it graphically. When such a curve is plotted, it -will be noted that at two-thirds radial penetration of the filament, about 90% of the filament volume has been penetrated.

The presently available evidence indicates that for maximum enhancement of dyeability the concentration of the acid and the application conditions should be such that than with the corresponding dry yarns in order to obtain the same degree of relaxation. However, the practical difficulties in handling the yarn through the relaxing step are usually greater with gelled yarn, since the break load of the yarn entering the relaxation bath is less than with the corresponding dry yarn. Since the relaxation treatment itself reduces momentarily the break load, yarn breakdown during treatment is generally more of a problem in treating gelled yarn.

The surprising and unobvious fact that dry or gelled multifilament yarn of synthetic polymer of the kind treated in accordance with this invention does not break down on passage through an aqueous solution of sulfuric acid containing about 56% by weight of H even at a residence time of 3 minutes, strongly indicates that the fiber maintains much of its structural integrity close to the point of solution. As indicated hereinbefore, one of the requirements for maximum dyeability improvement at short residence times appears to be the treatment of the fiber with the acid-treating agent under conditions, including concentration of acid, close to (sometimes extremely close to) those required to dissolve the fiber.

The molecular mechanism by which a change in fiber properties takes place during a relaxation treatment in accordance with this invention cannot be set forth with certainty. While the results described in the foregoing examples seem to show a relationship between the presence of voids in the filamentary material and its resistance to dyeing, our more recent work indicates that this structural barrier to dyeing does not result primarily from the presence of voids. We have found that filaments of synthetic polymers that are treated in accordance with this invention, and which are nearly void-free as spun, dye poorly and must be relaxation-treated in order to obtain dye-receptivity of commercial acceptability.

It is believed that, when the present invention is practiced, most of the molecular rearrangement responsible for the enhanced dyeability takes place within the amorphous regions of the fiber. The characteristic, definite changes in X-ray pattern, which involve crystalline portions of the fiber, must then represent only a small portion of the total rearrangement. Lacking in many cases a knowledge of the crystal structure of the polymer, one can say with respect to the crystal portions only that the change involves some alteration of sidewise packing of the chains within the unit cell, with little or no change of repeat distance. Close examination of the X-ray patterns of the treated fibers listed in Table VII showed that the change in X-ray pattern coincided with the progressive penetration and clearing of the voids from the fiber. At intermediate treating times short of complete penetration, the X-ray pattern consisted of a mixture or superposition of the patterns of untreated and treated, completely cleared fibers. Optical examination of cross-sections likewise gives the impression of two co-existing phases or distinct structures in partially cleared fibers, with a sharp boundary between them.

Instead of polyhexamethylene terephthalamide (6-T) in making polymers and filamentary materials and other shaped articles therefrom, and relaxing such shaped articles by treating them with an aqueous solution of an inorganic acid of the kind used in practicing this invention, one may similarly make and treat shaped articles of the polyisophthalamides, e.g., polyethylene isophthalamide, polyhexamethylene isophthalamide, or of any other difiicultly-meltable polymer of the kind with which this invention is concerned and of which numerous examples have been given hereinbefore both broadly and specifically.

Unless otherwise stated all the dyeing tests with acid and disperse dyes described hereinbefore were carried out using microdyeing and analytical procedures. A description of these procedures follows:

F RMULATION OF BATH Acid dye Disperse dye 150 mg. dye in total volume of 150 mg. dye in total volume of 300 300 ml. distilled water. ml. distilled water.

Ailldzfsormie acid (90.9%) to obtain %g./1. Igepon T77, /g./l. Calgon.

Dyeing procedure The 300 ml. dyebath (in 1 pint mason jar) is preheated to the dyeing temperature (97 0). Then 110 mg. of fiber is introduced, and the individual jars are sealed and placed in a Launder-Ometer for 2 hours of dyeing at 97 C.

At the end of the dyeing time the dyeing is quenched by the addition of cold water. The samples are hot water rinsed and dried.

Analytical procedure Calculation wt. of sample (mg) It is to be understood that the foregoing detailed description is given merely by way of illustration and that many variations may be made therein without departing from the spirit of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of enhancing the acid and disperse dyereceptivity, luster and tensile properties of a filament consisting of a wet-spun difficultly-meltable condensation polymer having repeating amide units as an integral part of the polymer chain and a melting point above about 275 C. while producing a filament which does not develop a void structure which comprises spinning a solvent solution of said polymer into a liquid coagulating bath in which the said polymer is insoluble thereby to obtain filamentary material in gel state, the solvent in which the said polymer is dissolved being aqueous sulfuric acid containing at least 75% by weight of sulfuric acid, and the liquid coagulating bath into which the said solvent solution is extruded being aqueous sulfuric acid having a concentration lower than about down to 0% prior to said spinning and such that the solution of the polymer is coagulated into the form of gelled filamentary material, drawing said filaments in a draw ratio of 2.5 to 3.2; and preventing the formation of a void structure in said filament by substantially completely penetrating internally the freshly formed, unwashed and undried gelled filamentary material, without causing filament surface cracking, coalescence or fibrillation, with a shrinking agent in the form of an aqueous solution containing, by weight, from 51% to 59% H 50 for a period of at least second and at a temperature within the range of from ambient temperature to about 100 C.

2. The process of claim 19 wherein said condensation polymer is poly(hexamethylene adipamide).

3. The method of enhancing the acid and disperse dyereceptivity, luster and tensile properties of a filament consisting of a wet-spun difficultly-meltable condensation polymer having repeating amide units as an integral part of the polymer chain and a melting point above about 275 C. while producing a filament which does not develop a void structure which comprises spinning a solvent solution of said polymer into a liquid coagulating bath in which the said polymer is insoluble thereby to obtain filamentary material in gel state, the solvent in which the said polymer is dissolved being aqueous sulfuric acid containing at least by weight of sulfuric acid or aqueous phosphoric acid containing at least by weight phosphoric acid, and the liquid coagulating bath into which the said solvent solution is extruded being of the same acid composition of said solvent and having a concentration lower than in said aqueous solvent down to 0% prior to said spinning and such that the solution of the polymer is coagulated into the form of gelled filamentary material; drawing said filaments in a draw ratio of 2.5 to 3.2; and preventing the formation of a void structure in said filament by substantially completely penetrating internally the freshly formed, unwashed and undried gelled filamentary material, without causing filament surface crack ing, coalescense or fibrillation, with a shrinking agent selected from the group consisting of aqueous solutions of sulfuric acid, hydrochloric acid and phosphoric acid in the following ranges of concentration by weight:

(a) 51 to 58% H SO (b) 25 to 34% HCl, and

(c) 79 to 85% H PO for a period of time and at a temperature sufficient to improve the acid and disperse dye-receptivity thereof.

4. The process of claim 2 wherein said condensation polymer is poly(hexamethylene adipamide).

(References on following page) X percent dyestuif.

21 22 References Cited 3,228,745 1/1966 Galatioto 8130.1 3 389 206 6/1968 Jamison 264 341X E N J a UNITED STAT S FATE TS 3,296,341 3/1967 Briar et a1. 264--342X 8/1941 Watson 28-728 ,269,970 8/1966 Epstein et a1 264184 10/1962 Smith 2876 10/1964 Cipriani o ,s 5 W Prlrnary Examlner 7/1941 Finzel 264168X I. MORRIS, Assistant Examiner 10/1944 Dreyfus et a1 264--168X 1/1966 Cipriani 264-203 US. Cl. X.R. 10/1964 Denyes 264-169 11/1966 ROSGIIthaI 26029.2 26448184342 8430-1 W UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,558,763 Dated January 26, 1971 Inventor(s) R. G Quynn et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 23, after "polytetramethylene terephthalamide insert polyethylene terephthalamide.

Column 6, line 34, "wit" should be --with.

Column 6, line 44, "film" should be deleted.

Column 6, line 50, "filns" should be deleted.

Column 7, line 4, "film" should be deleted.

Column 7, line 24, "above" should be --about---.

Column 7, line 49, "inventory" should be -invention---.

Column 11, Table III, under Bath Concentrations, "H 50 shot be ---H SO Column 11, Table IV A, "Strength Roll Rinse" should be Stretch Roll Rinse--.

Column 12, line 39, "6080" should be ---60-68--.

Claim 2, first line, "19" should be ---l--.

Claim 4, first line, "2" should be ---3--.

Signed and sealed this 1 7th day of August 1 971 (SEAL) Attest:

EDWARD M.FIETCHER,JR. WILLIAM E. SGHUYLER, JR. Attesting Officer Commissioner of Patents 

